AU7928198A

AU7928198A - Method for electronically selecting the dependency of an output signal from the spatial angle of acoustic signal impingement and hearing aid apparatus

Info

Publication number: AU7928198A
Application number: AU79281/98A
Authority: AU
Inventors: Joseph Maisano
Original assignee: Phonak AG
Current assignee: Sonova Holding AG
Priority date: 1997-07-16
Filing date: 1998-07-14
Publication date: 1999-02-10
Anticipated expiration: 2018-07-14
Also published as: EP0997055B1; DE69805526D1; EP0802699A2; IL133999A0; TR200000119T2; WO1999004598A1; EP0802699A3; CA2296414A1; IL133999A; AU749652B2; EP0997055A1; CN1267444A; CA2296414C; KR20010021877A; NZ502350A; ATE218025T1; DK0997055T3; DE69805526T2; JP2001510975A

Abstract

For beam forming acoustical signals the phase difference of the output signals of two acoustical/electrical transducers is determined (27) and is multiplied by a factor (30). One of the two output signals of the at least two transducers is phase shifted by an amount according to the multiplication result. This phase shifted signal and the signal of the second transducer are led to a signal processing unit, wherein beam forming on these at least two signals is performed. Thereby, it becomes possible to perform beam forming as if the transducers were mutually distant by more than they physically are. <IMAGE>

Description

WO99/04598 PCT/IB98/01069 - 1 Method for electronically selecting the dependency of an output signal from the spatial angle of acoustic signal impingement and hearing aid apparatus The present invention is generically directed on a technique 5 according to which acoustical signals are received by at least two acoustical/electrical converters as e.g. by multidirec tional microphones, respective output signals of such convert ers are electronically computed by an electronic transducer unit so as to generate an output signal which represents the 10 acoustical signals weighted by a spatial characteristic of am plification. Thus, the output signal represents the received acoustical signal weighted by the spatial amplification charac teristic as if reception of the acoustical signals had been done by means of e.g. an antenna with an according reception 15 lobe or beam. Thus, the present invention is generically di rected on an electronically preset, possibly electronically ad justed and tailored reception "lobe". Figure 1 most generically shows such known technique for such "beam forming" on acoustical signals. Thereby, at least two 20 multidirectional acoustical/electrical converters 2 a and 2 b are provided, which both - per se - convert acoustical signal irre spective of their impinging direction 0 and thus substantially unweighted with respect to impinging direction 0 into first and second electrical output signals Al and A,. The output signals 25 Al and A 2 are fed to an electronic transducer unit 3 which gen erates from the input signals A, A 2 an output signal A,. As shown within the block of unit 3 the signals A, 2 are treated to result in the result signal Ar which represents either of A or A2, but additionally weighted by the spatial amplification 30 function F1(0). Thus, acoustic signals may selectively be am CONFIRMATION COPY WO 99/04598 PCT/IB98/01069 - 2 plified dependent from the fact under which spatial angle 0 they impinge, i.e. under which spatial angle the transducer ar rangement 2a, 2b "sees" an acoustical source. Thereby, such known approach is strictly bound to the physical location and 5 intrinsic "lobe" of the converters as provided. One approach to perform signal processing within transducer unit 3 shall be exemplified with the help of Fig. 2. Thereby, all such approaches are based on the fact that due to a prede termined mutual physical distance p, of the two converters 2 a 10 and 2 b, there occurs a time-lag dt between reception of an acoustical signal at the converters 2 a, 2 b* Considering a single frequency - o - acoustical signal, re ceived by the converter 2 a, this converter will generate an output signal 15 (1) Al = A sint, whereas the second transducer 2 b will generate an output signal according to (2)

A

2 = A' sin(o(t+dt), whereat dt is given by psinO 20 (3) dt = in C therein, c is the sound velocity. By time-delaying e.g. A, by an amount (4) T = pp/c WO 99/04598 PCT/IB98/01069 - 3 and forming the result signal A, from the difference of time delayed signal Al' - as a third signal - namely from (5) A,' = A sino (t+T), and (2) A 2 = A sino (t+dt), 5 there results, considered at the frequency 0, a spatially car doid weighted output signal Ar as shown in the block of trans ducer unit 3: (6) ArJ = IA,' - A 2 = 2A sin(o (T-dt)/2) = 2A sin((o (T-p,*sinO/c)/2) 10 At 0 = 900 Ar becomes zero and at 0 = -9 0 0 Ar becomes (7) Arma = 2A sin o p,/c. Such processing of the output signals of two omnidirectional order converters leads to a first order cardoid weighing func 15 tion F,(O) as shown in Fig. 3. By respectively selecting con verters with higher order acoustical to electrical conversion characteristic i.e. "lobe" and/or by using more than two con verters, higher order - m - weighing functions Fm(O) may be re alised. 20 In Fig. 4 there is shown the amplitude Ama-characteristic, re sulting from first order cardoid weighing as a function of fre quency f = o/2n. Additionally, the respective function for a second order cardoid weighing function F 2 (0) is shown. Thereby, there is selected a physical distance p, of the two converters 25 2a and 2 b of fig. 1 to be 12 mm.

WO99/04598 PCT/IB98/01I069 - 4 As may clearly be seen at a frequency f, which is (8) f = c/(4pp) maximum amplification occurs of +6 dB at the first order car doid and of +12 dB at a second order cardoid. For pp, = 12 mm, 5 f, is about 7 kHz. From fig. 4 a significant roll-off for low and high frequencies with respect to f, is recognised, i.e. a significant decrease of amplification. Techniques for such or similar type of beam forming are e.g. 10 known from the US 4 333 170 - acoustical source detection -, from the European patent application 0 381 498 directional mi crophone - or from Norio Koike et al., "Verification of the Possibility of Separation of Sound Source Direction via a Pair of Pressure Microphones", Electronics and Communications in Ja 15 pan, Part 3, Vol. 77, No. 5, 1994, page 68 to 75. Irrespective of the prior art techniques used for such beam forming with at least two converters, the distance pp is an im portant entity as may be seen e.g. from formula (8) and di rectly determines the resulting amplification/angle dependency. 20 Formula (8) may be of no special handicap if such a technique is used for narrow band signal detection or if no serious lim its are encountered for geometrically providing the at least two converters at a large mutual physical distance pp. Nevertheless, and especially for hearing aid applications, the 25 fact that f, is inversely proportional to the physical distance pp of the transducers is a serious drawback, due to the fact that for hearing aid applications the audio frequency band up WO 99/04598 PCT/IB98/01069 - 5 to about 4 kHz for speech recognition should be detectable by the at least two transducers which further should be mounted with the shortest possible mutual distance pp. These two re quirements are in contradiction: The lower f, shall be real 5 ised, the larger will be the distance pp required. It is thus a first object of the present invention to remedy the drawbacks encountered with respect to p,-dependency of known acoustical "beam forming". The first object of the present invention is reached by provid 10 ing a method for electronically selecting the dependency of an electric output signal of an electronic transducer unit from spatial direction wherefrom acoustical signals impinge on at least a first and a second acoustical/electrical converter, connected to the inputs of said transducer unit, thereby input 15 ting first and second electric signals thereto, which comprises the steps of * generating at least one third electric signal in dependency from mutual phasing of the first and the second electric sig nals, said phasing being multiplied by a constant or a fre 20 quency-dependent factor and further from a fourth electric signal which depends from at least one of the first and the second electric signals; * generating the output signals of the transducer unit in de pendency of the third signal and further from a fifth elec 25 tric signal which is dependent from at least one of the first and the second electric signals. Thereby, it becomes possible, irrespective of the actual physi cal mutual distance of the two converters, to select said de- WO 99/04598 PCT/IB98/01069 - 6 pendency, thereby pre-selecting same and possibly tuning and adjusting same, to result in a dependency as if the at least two converters were physically arranged at completely different physical positions than they really are. 5 In a first preferred manner of realising the inventive method the fourth electric signal is selected to be linearly dependent only from one of the first and second electric signals, thereby being preferably directly formed by such first or second elec tric signal. 10 Nevertheless, in a today's more preferred manner of realising the inventive method, the fourth electric signal is dependent on both first and second electric signals. In a preferred form the fourth electric signal has a predetermined or adjustable "lobe" characteristic, i.e. dependency from spatial impinging 15 direction. Thereby in a preferred form of "lobe" realisation the fourth electric signal is generated by delaying one of the first and second signals and then summing the delayed signal and the other, undelayed signal of said first and second sig nals. Thereby, the fourth electric signal per se has an ampli 20 fication to impinging angle dependency and thus defines - as was said - for a "lobe", as an example according to a depend ency as was discussed with the help of the figs. 1 to 4. In a further preferred form of realising the inventive method, either per se or combined with either method to generate the 25 fourth signal as just stated, and especially combined with gen erating the fourth signal with a "lobe"-characteristic, it is proposed to generate the fifth electric signal in direct or linear dependency of at least one of the first and second elec- WO 99/04598 PCT/IB98/01069 - 7 tric signals, thereby preferably using one the said first and second electric signals as the fifth electric signal. Thereby, and again per se or combined with either method of generating the fourth electric signal, especially combined with 5 generating the fourth electric signal with a "lobe"-dependency, it is proposed to generate the fifth electric signal as well with a "lobe" dependency from spatial impinging angle, which is realised in a first form by delaying one of the first and sec ond signals and summing the delayed signal and the other of 10 said first and second signals. Thereby, it becomes clear that the fourth electric signal, generated to define for a "lobe" characteristic, may directly be used as the fifth electric sig nal, having then the same "lobe"-characteristic. In a further, clearly preferred realisation form of the inven 15 tive method and combined with any of the preferred realisation forms stated up to now and throughout the further description, it is proposed to generate the first and second electric sig nals in their respective spectral representation, thereby gen erating the at least one third electric signal in dependency of 20 mutual phasing of respective spectral components of the first and second signals and multiplied by a constant frequency-inde pendent or by frequency-dependent factors. In a further preferred mode of operation, the frequency dependent multiplication factors are selected to be inversely 25 proportional to frequency, at least in a first approximation. With an eye specifically on hearing aid applications, wherefore the present method is most suited, but may be clearly applied to others, it is proposed that the real physical distance of the first and second converters to be at most 20 mm, whereby WO 99/04598 PCT/IB98/01069 -8 the virtual distance, which is at least dependent from the phasing multiplication factor, is selected to be larger than the mutual physical distance of the two converters, in other words dependency of the transducer unit's outputsignal from 5 spatial angle becomes so as if, physically, converters were provided at considerably larger mutual distances than they really are. It goes without saying, that such technique is of very high advantage in any space-restricted applications, as especially in hearing aid applications. 10 To resolve the object mentioned above and to realise especially a hearing aid, whereat, irrespective of the physical position of at least two acoustical/electrical converters, a desired re ception lobe may be tailored and possibly adjusted according to the needs, is realised inventively by an acoustical/electrical 15 transducer apparatus comprising at least two acoustical/elec trical converters spaced from each other by a predetermined physical distance, whereby the at least two converters gener ate, respectively, first and second electrical output signals and wherein the outputs of said acoustical/electrical convert 20 ers are operationally connected to an electronic transducer unit, which generates an output signal dependent from said first and second output signals of said converters by an ampli fication function which function is dependent from spatial an gle under which said converters receive acoustical signals, 25 comprising: - a phase difference detection unit, the inputs thereof being operationally connected to the outputs of said converters and generating at its output a phase difference-dependent signal, WO 99/04598 PCT/IB98/01069 - 9 - a phase processing unit, one input thereof being operation ally connected to the output of said phase difference detection unit, at least one second input of said processing unit being operationally connected to a factor-value 5 selecting source, a third input of said phase processing unit being operationally connected to at least one of the inputs of said at least two converters, said phase processing unit generating an output signal at its output according to a signal at said third input with a phasing according to a sig 10 nal at said one input and at said at least one second input, - a beam-former processing unit with at least two inputs, one input being operationally connected to the output of said phase-processing unit, the second input being operationally connected to at least one output of said at least two con 15 verters. Under all the aspects of the invention there is thus possible to realise (9) Pv > Pp. This especially for low-space applications, as especially for 20 hearing aid applications. Thereby, there is introduced the virtual distance Pv of trans ducers, i.e. the distance of converters which would have to be physically realised to get an angle dependency as realised in ventively. 25 Thereby, according to formula (8), f, may be shifted to lower frequencies: WO99/04598 PCT/IB98/01069 - 10 It becomes possible to realise fr values well in the audio frequency band for speech recognition (< 4 kHz) with physical distances of microphones, which are considerably smaller than this was possible up to now. 5 Multiplying the phase difference by a constant factor does nev ertheless not affect the roll-off according to fig. 4. This roll-off is significantly improved, leading to an enlarged fre quency band B, according to fig. 4 if - as was said - the pre determined function of frequency is selected as a function 10 which is at least in a first approximation inversely propor tional to the frequency of the acoustic signal. For instance for the first order cardoid according to fig. 3 and fig. 4, there may be reached a flat frequency characteris tic between 0,5 and 4 kHz and thus a significantly enlarged 15 frequency band Br with well-defined roll-offs of amplification at lower and higher frequencies by accordingly selecting the frequency dependent function to be multiplied with the phase difference. Other objects of this invention will become apparent as the de 20 scription proceeds in connection with the accompanying draw ings, of which show: Fig. 1: A functional block diagram of a two-transducer acous tic receiver with directional beam forming according to prior art; 25 Fig. 2: one of prior art beam forming techniques as may be incorporated in the apparatus of fig. 1, shown in block diagram form; WO99/04598 PCT/IB98/0 1069 - 11 Fig. 3: a two-dimensional representation of a three dimensional cardoid beam, i.e. amplification charac teristic as a function of incident angle of acousti cal signals; 5 Fig. 4: the frequency dependency of the maximum amplification value according to fig. 3 for first and second order cardoid functions; Fig. 5: a pointer diagram resulting from the technique ac cording to fig. 2, still prior art; 10 Fig. 6: a pointer diagram based on fig. 5 (prior art), but according to the inventive method, which is performed by an inventive apparatus; Fig. 7: a simplified block diagram of a first realisation form of an inventive apparatus, especially of an in 15 ventive hearing aid apparatus, wherein the inventive method is implemented; Fig. 8: a simplified block diagram of a today preferred re alisation form of the inventive method and apparatus; Fig. 9: a simplified block diagram of an inventive apparatus, 20 operating according to the inventive method, in a generalised form; Fig. 10: a generic signal-flow/functional block diagram of an inventive apparatus operating according to the inven tive method; WO99/04598 PCT/IB98/01069 - 12 Fig. 11: the measured directivity characteristics resulting from the inventive method and inventive apparatus ac cording to fig. 8; Fig. 12: a second directivity characteristics in a representa 5 tion according to fig. 11, resulting from the inven tive method and apparatus according to fig. 8. As was mentioned above, in the figs. 1 to 4 known beam forming techniques were based on at least two acoustical/electrical transducers spaced from each other and directly on their mutual 10 physical distance pp. In fig. 5 there is shown a pointer diagram according to (6). The basic idea of the present invention shall be explained now with the help of the still simplified one - o - frequency ex ample. The inventively realised pointer diagram is shown in 15 fig. 6. The phase difference - dt between signal A, and A, ac cording to fig. 6 is (10) o dt = Ps - AP. C This phase difference is determined and is multiplied by a value dependent from frequency, thus with the respective value 20 of a function M(o), which may be also a constant M 0 # 1. By phase shifting one of the two signals A, A 2 according to the respective pointers in fig. 6, e.g. of A 2 by M( " A or by Mo Ap, there results the phase shifted pointer A2v. This pointer would 25 have also occurred if dt had been larger by an amount according WO 99/04598 PCT/IB98/01069 - 13 to M, or M 0 , thus if a "virtual transducer" had been placed distant from transducer 1 a by the virtual distance Pv, for which: (11) Pv = M. pp or 5 (12) Pv = Mo Pp. As we consider one single frequency for simplicity we may write

M

0 = M'. With virtual TV (13) tv, = M " T and sinO 10 (3 v ) dt v = M. pp C we get according to the present invention: (1i v ) A = Alr = Asinot (2 v ) A2v = Asinc (t+dt v ) = Asino (t+M 0 dt) (5

V

) A 1 v = Asino(t+Mt) 15 (6 v ) Arv= 2Asin ( (M - o(T-dt)/2) With (8) we further get: c 1 fv -- =f. 4 Mmpp M r Therefrom, we may see that for a given pp, which would lead to a too high fr, frv is reduced by the factor M, taken M, > 1. 20 In fig. 7 there is schematically shown a first preferred reali sation form of an inventive apparatus in a simplified manner, WO99/04598 PCT/IB98/01069 - 14 especially for implementing the inventive method into an inven tive hearing aid apparatus. Thereby, the output signals of the acoustical/electrical transducer 2 a and 2 b are fed to respec tive analogue to digital converters 20a, 20b, the outputs 5 thereof being input to time domain to frequency domain - TFC converter units as to Fast-Fourier Transform units 22a and 22b. A spectral phase difference detecting unit 27 spectrally de tects phase difference AT, for all n spectral frequency compo nents which are then multiplied by a set of constants c. If M 10 is a function of o, Me, then the c n can be different for dif ferent frequencies, and represent a frequency dependent func tion or factor. If on the other hand the phase differences Apn are multiplied by the same c o = cn # 1 this accords with using a constant M 0 . 15 This multiplication according to (3,) is done at a spectral multiplication unit 28. Signal A, in its spectral representa tion is then spectrally phase shifted at a spectral phase shifter unit 29 by the multiplied spectral phase difference signals output by multiplier unit 28. 20 According to fig 7 the signal A, in its spectral representation and inventively, spectrally phase shifted - A(o,Ag' n ) - is computed in a spectral computing unit 23 together with A 2 in its spectral representation, as if transducer 2a was distant from transducer 2b by a distance Pv = Mp. The resulting spec 25 trum is transformed back by a frequency to time domain con verter - FTC - as by an Inverse-Fast-Fourier-Transform unit 24 to result in A,.

WO99/04598 PCT/IB98/01069 - 15 Thereby, other beam forming techniques than that described with the help of figs 1 to 4, i.e. using the time delaying technique - transformed in the frequency domain - may be used in unit 23. Nevertheless the time delaying technique is preferred. 5 With an eye on fig. 4 it has been explained that by inventively introducing "virtual" converters with a virtually enlarged mu tual distance, it becomes possible to shift the high gain fre quency fr towards lower frequencies, which is highly advanta geous especially for hearing aid applications. This is already 10 reached if instead of a frequency dependent function M,, a con stant M 0 is multiplied with the phase difference as explained. In a preferred mode of the invention the frequency dependent function M. is selected to be, at least in a first approxima tion, 1 15 (14) M( (0 Thereby, it is reached that, different from fig. 4, there will be no roll-off and the gain in target direction will be con stant over the desired frequency range. By appropriately se lecting the function M. it is e.g. possible to reach a flat 20 characteristic within a predetermined frequency range, e.g. be tween 0.5 and 4 kHz with defined roll-offs at lower and higher frequencies. With appropriately selecting the function M, prac tically any kind of beam forming can be made. For generating higher order cardoid weighing functions it is 25 absolutely possible to additionally use the not phase-shifted output signal A, - as shown in fig. 7 by dotted line - as com- WO99/04598 PCT/IB98/01069 - 16 puting input signal to unit 23 too, thus "simulating" three converters. Fig. 8 shows a today's preferred embodiment of an inventive ap paratus in a functional-block/signal-flow representation in 5 analogy to the representation of fig. 7. Blocks and signals which were already explained with the help of fig. 7 are de fined in fig. 8 by the same reference numbers. The phase spectrum at the outside of multiplication unit 28, A'...n is added at a summing unit 29' to a signal Akr ,...n( ), 10 also in spectral representation, which signal has a preselected dependency from impinging angle 0, as especially a first or higher order cardoid dependency. To realise that signal Akrl ... n(~ 1...n,0) and following the expla nation with respect to figures 2 to 4, the output signal A,(w), 15 and A 2 ((o) in their spectral representation, are led to a beam former unit 32, which may be integrated in beam-former unit 23' and which e.g. is built up according to the beam-former of fig. 2. Thereby, it must be clearly stated that instead of the beam former 32 as shown in fig. 8 other kinds of beam-former result 20 ing in different than first order cardoid characteristics may be implemented there. The spectrum Akr,1...n(O..n,0) is then phase-shifted by the phase adding unit 29' by Ap's...n, resulting in an output signal of that unit 29' which is the spectrum A ..n(p .nAp..' nO) as 25 shown in fig. 8. The signal Ak,1...n(o...n,O) as well as the out put signal of summing unit 29' are led to the beam-former unit 23', where they are preferably again summed as shown at 33.

WO99/04598 PCT/IB98/01069 - 17 At the output of beam-former unit 32 a signal is generated with a real cardoid dependency from impinging angle 0, whereas at the output of unit 29', and thus after phase shifting, a de pendency function with respect to impinging angle 0 is realised 5 according to virtually positioned converters. When summing, as with the unit 33 within beam-former unit 23', there results a dependency of the output signal A, from impinging angle 0 ac cording to a second order cardoid if the real cardoid depend ency at the output of unit 32 is a first order cardoid. 10 Thus, in a more generic representation, as shown in fig. 9, the phase difference spectrum at the output of unit 27 is subjected to a phase shifter unit 35, where it is modified as per c, to

C

n The generalised phase shifter 35 may receive directly one of 15 the output signals of one of the two converters 2a, 2b and/or a signal which results from beam forming from the said converter output signals to be phase shifted. In fig. 9 this is repre sented by the signal path fed back from beam former 37 to the phase shifter 35. This feedback accords, with an eye on fig. 8, 20 to the signal path between beam former 32 and summing unit 29'. According to fig. 9 beam former unit 32 of fig. 8 is integrated in the overall beam former unit 37. The beam former 37 in its generalised form of fig. 9 receives at least one of the output signals of the converters 2a, 2b and 25 the output signal of the generalised phase shifter 35. It is evident for the skilled artisan that * more than two real converters may be used and/or WO99/04598 PCT/IB98/01069 - 18 * more than one M. function or of c o or c ...

n sets may be used to produce more than one "virtual transducer" signal from one or from more than one real converter signals respectively. With selecting the number of physical and virtual converters, 5 their characteristics and virtual "relocation" of these con verters, the spatial weighing function may be selectively tai lored. The present invention under its principal object makes it pos sible to realise practically any desired beam forming with at 10 least two converters separated by only a predetermined small distance, due to the fact that electronically there is provided a virtual mutual converter location of the physically provided converter. Thereby, roll-off may be significantly reduced by such virtual 15 transducer, which is especially established with realising a virtual distance of the converter which is dependent from fre quency, especially inversely dependent. By selecting a fre quency-M, 0 -dependent virtual distance of the converters, virtu ally an array of frequency-selective converters is established. 20 For a hearing aid apparatus the real distance between the at least two transducers, i.e. microphones, is selected to be 20 mm at most, preferably less. Fig. 10 shows in most generic form the principle proceeding and apparatus structure as according to the present invention and 25 common to all embodiments of the invention as described above. First and second electric signals S 1 and S 2 , which are derived from the output signals of the at least two acoustical/electri cal converters 2 a

,

2 b

,

are input to the transducer unit 3.

WO99/04598 PCT/IB98/01069 - 19 Within unit 3, there is provided a phase difference detection unit according to unit 27 of figures 7, 8 or 9. The phase dif ference detection unit 27 has respective inputs which are op erationally connected to the inputs of unit 3 and thus to the 5 outputs of the converters 2a, 2b. The output of the phase dif ference detection unit 27 is operationally connected to an in put of a phase processing unit 40 shown in dashed-dotted lines in fig. 10. The phase processing unit has a second input, which is connected to a factor value-selecting source 42, generating 10 a constant or frequency-dependent factor h. A third input of the phase processing unit is operationally connected as sche matically shown by combining unit 44 in an "AND" or in an "EX OR" dependency to respective outputs of the at least two con verters 2 a and 2 b . The phase processing unit 40 generates an 15 output signal, S 3 , in accordance with a signal, S 4 , applied to the third input of the processing unit 40 and in accordance with the signals applied to the first - from 27 - and second from 42 - inputs to the phase processing unit. The signal at the first input of the phase processing unit, 20 which is operationally connected to the output of the phase difference detection unit, is multiplied - by unit 28 - by the constant or frequency-dependent factor, and, at a signal com bining unit 46, the output signal of the processing unit, sig nal S 3 , is thus generated in dependency from mutual phasing of 25 the output signals of the converters, multiplied by a constant or frequency-dependent factor and from signal S 4 as applied to the third input of the processing unit 40, which latter signal

S

4 is dependent from at least one of the output signals of the converters 2a

,

2 b

.

In unit 46 the dependency F, of signal S 3 WO99/04598 PCT/IB98/01069 - 20 from both, signal S 4 and multiplied phasing signal as at the output of unit 28, is generated. The signal S3, which accords to A,(o) of fig. 7 or to Akr,1...n()1...nO) of figs. 8 and 9, is input to a beam former 5 processing unit 48 according.to unit 23 or 23' or 37, as of the figs. 7 to 9. The beam former processing unit comprises a sec ond input to which S5, dependent from at least one of the out put signals of the converters 2 a, 2 b is fed. Latter signals are thus operationally connected as schematically shown by block 50 10 in an "EX-OR" or in an "AND" combination to the beam former processing unit 48. In fig. 11 there is shown the "lobe" or directivity character istic - in dB - which was measured at an inventive apparatus according to fig. 8 at single frequency 1 kHz of acoustical 15 signals impinging on the two acoustical/electrical converters 2 a, 2 b. In this apparatus there was valid: converters 2 a, 2 b: omnidirectional microphones, KNOWLES EK 7263 Physical distance pp: 12 mm 20 T: 35 psec. c: 2 at 1 kHz and at 4 kHz There resulted a directivity index as defined in SPEECH COMMU NICATION 20 (1996), 229 to 240, Microphone array systems for hands-free telecommunication, Gary W. Elco of 8.83. 25 In fig. 12 the result is shown at an inventive apparatus which was used for the measurement according to fig. 11, but at 4 kHz WO99/04598 PCT/IB98/01069 - 21 single frequency acoustical impinging signals. The directivity index became 7.98. There results from proceeding according to fig. 8 a directivity characteristics according to a second order cardoid. This would 5 conventionally have to be realised by means of four acousti cal/electrical converters as of 2 a and 2 b , which four convert ers define for a spacing of 24 mm between respective two of the four converters. Thus, it might be seen that with the inventive method and apparatus with only two acoustical/electrical con 10 verters with a mutual spacing of 12 mm a directivity result is reached as if four acoustical/electrical converters had been used with mutual spacing of 24 mm.

Claims

1. A method for electronically selecting the dependency of an electric output signal of an electronic transducer unit from spatial direction wherefrom acoustical signals impinge on at 5 least a first and a second acoustical/electrical converter op erationally connected to the input of said transducer unit and thereby inputting first and second electric signals thereto, comprising the steps of * generating at least one third electrical signal in dependency 10 from mutual phasing of said first and second electric signals multiplied by a constant or a frequency-dependent factor and further from a fourth electric signal which is dependent from at least one of said first and second electric signals; * generating said output signal of said transducer unit in de 15 pendency of said third electric signal and a fifth electric signal being dependent from at least one of said first and second electric signals.

2. The method of claim 1, thereby generating said fourth electric signal as a signal dependent from said first or second 20 electric signal.

3. The method of claim 1, thereby generating said fourth electric signal as dependent from said first and said second electric signals.

4. The method of claim 1, thereby generating said fourth 25 electric signal as a signal with a predetermined or adjustable dependency from said spatial direction, as with a cardoid de pendency. WO99/04598 PCT/IB98/01069 - 23 5. The method of claim 1, thereby generating said fourth electric signal by delaying one of said first and second elec tric signals and summing the delayed signal and the other of said first and second signals.

5

6. The method of one of claims 1 to 4, thereby generating said fifth electric signal as being dependent from one of said first and second electric signals.

7. The method of one of claims 1 to 4, thereby generating said fifth electric signal as dependent from both said first 10 and said second electric signals.

8. The method of one of claims 1 to 5 or 7, thereby generat ing said fifth electric signal as a signal with a predetermined or adjustable dependency from said spatial direction, as with a cardoid dependency. 15

9. The method of one of claims 1 to 5 or 7 or 8, thereby gen erating said fifth electric signal by delaying one of said first and of said second signals and summing said delayed sig nal and the other of said first and second signals.

10. The method of one of claims 1 to 9, thereby generating 20 said fourth electric signal by generating said fifth electric signal.

11. The method of one of claims 1 to 10, thereby generating said first and second electric signals in their respective spectral representation and generating said at least one third 25 electric signal in dependency of mutual phasing of respective spectral components of said first and second signals, multi plied by said factor and in dependency of said fourth electric signal. WO99/04598 PCT/IB98/01069 - 24

12. The method of one of claims 1 to 11, thereby selecting said factor as inversely proportional to frequency.

13. An acoustical/electrical transducer apparatus comprising at least two acoustical/electrical converters spaced from each 5 other by a predetermined physical distance, whereby the at least two converters generate, respectively, first and second electrical output signals and wherein the outputs of said acoustical/electrical converters are operationally connected to an electronic transducer unit, which generates an output signal 10 dependent from said first and second output signals of said converters by an amplification function which function is de pendent from spatial angle under which said converters receive acoustical signals, comprising: - a phase difference detection unit, the inputs thereof being 15 operationally connected to the outputs of said converters and generating at its output a phase difference-dependent signal, - a phase processing unit, one input thereof being operation ally connected to the output of said phase difference detection unit, at least one second input of said processing 20 unit being operationally connected to a factor-value selecting source, a third input of said phase processing unit being operationally connected to at least one of the outputs of said at least two converters, said phase processing unit generating an output signal at its output according to a 25 signal at said third input with a phasing according to a sig nal at said one input and at said at least one second input, - a beam-former processing unit with at least two inputs, one input being operationally connected to the output of said phase-processing unit, the second input being operationally WO99/04598 PCT/IB98/01069 - 25 connected to at least one output of said at least two con verters.

14. The apparatus of claim 13, wherein said factor value selecting source generates a constant or frequency-dependent 5 signal values.

15. The apparatus of claim 13 or 14, wherein said third input of said phase-processing unit is operationally connected to one output of said at least two converters.

16. The apparatus of one of claims 13 to 15, wherein said 10 third input of said phase-processing unit is connected to the output of a beam former unit, the inputs thereof being opera tionally connected to the outputs of said at least two convert ers.

17. The method of claim 16, said beam former unit comprising a 15 further summing unit, one input thereof being operationally connected to an output of one of said at least two converters, the other input thereof being operationally connected via a time-delay unit to the output of the other of said at least two converters. 20

18. The apparatus of one of claims 13 to 17, wherein said sec ond input of said beam-former processing unit is operationally connected to one of said at least two converters.

19. The apparatus of one of claims 13 to 18, wherein said sec ond input of said beam-former processing unit is operationally 25 connected to the output of a summing unit, one input thereof being connected via a time-delaying unit to the output of one of said at least two converters, a second input of said summing WO99/04598 PCT/IB98/01069 - 26 unit being operationally connected to the output of said second one of said at least two converters.

20. The apparatus of one of claims 13 to 19, wherein the out puts of said at least two converters are operationally con 5 nected to the inputs of a further summing unit, one thereof via a time-delay unit, the output of said further summing unit be ing operationally connected to said third input of said phase processing unit and to said second input of said beam-former processing unit. 10

21. The apparatus of one of claims 13 to 20, wherein the out puts of said at least two converters are generated via respec tive analogue to digital converters and time domain to fre quency domain transform units, said phase-difference detection unit, said phase-processing unit and said beam-former process 15 ing unit operating in frequency domain, the output of said transducer unit being generated via a frequency domain to time domain conversion unit.

22. The apparatus of one of claims 13 to 21, being a hearing aid apparatus, said at least two converters having a mutual 20 physical distance of at most 20 mm.